Not Applicable
Not Applicable
1. Field of Invention
This invention pertains to a particulate removal system and an apparatus for entrapment and collection of particulate material from gases. More particularly, this invention pertains to a vacuum apparatus providing criticality safe collection of radioactive particles entrained in gas and a transport vehicle for safe storage and transport of the vacuum apparatus having collected radioactive materials therein in order to protect an operator.
2. Description of the Related Art
Typical of prior art devices are shop vacuums that are modified to include dust collection reservoirs that are of limited internal size in order to collect fissionable materials in particulate form within the shop vacuum, which is disposed of as a complete unit identified as radioactive waste. A prior art device includes a conventional vacuum head motor attached to a container having mesh filter bags within the container. The mesh filter bags are oriented within the container with air filtering through each bag and into an internal bottle or small-sized container that is made of metal mesh or a material sized to minimize criticality reactions between radioactive particles entrapped by the filter bags. The mesh filter bags require periodic removal for replacement or cleaning, and the internal bottle or small-sized container typically requires periodic removal for replacement. The operator is potentially exposed to radioactive particles during opening of the outer container, replacement of internal containers, and during any attempts at cleaning of the vacuum pickup device, unless the device is maintained within a sealed glove box. If positioned within a glove box, the vacuum pickup device fails to provide mobility, due to the sizing of the device to fit within glove boxes utilized in nuclear reactor facilities and/or in glove boxes at a facility that manages fissionable materials. Once placed within a glove box, the vacuum pickup device is not generally cleaned and removed, but is disposed of as radioactive contaminated waste after the radioactive particles are removed for recycle or for disposal.
Another prior art device is a vacuum pickup device including a centrally positioned vacuum motor that is in fluid flow communication with one or a plurality of vertically oriented, spaced apart canisters having a filter bag in each canister. A high efficiency particulate (HEPA) filter is located intermediate of the centrally positioned vacuum motor, such as in an elongated central container, with the HEPA filter in fluid flow communication between the canisters and the vacuum motor. When air or liquid containing radioactive particles is drawn into an intake hose, the air or liquid travels through one cannister or the plurality of canisters, through the central container, through the HEPA filter, for exiting from exhaust ports proximal to the vacuum motor. The vacuum pickup device fails to provide easily accessible filter bags in each canister for replacement, and provides a HEPA filter positioned to require periodical opening of the central container for visual checking for accumulation of radioactive materials to determine the need for replacement before a criticality reaction occurs. Repetitive visual inspections of the canisters, and/or monitoring of changes in air pressure through the prior art device, suggestive of filter clogging, requires frequent maintenance by an operator of the vacuum pickup device.
Another prior art device is a cyclonic vacuum generator including a canister having a hole or opening into which debris laden air is received for distribution through a central area of the canister. At least two internal conical members and a cone filter shroud guides the flow of debris laden air through a nonlinear path downwards within the canister in order to direct the air flow through low pressure areas to direct debris downwards into the lower portion of the canister. Additionally, internal flutes are positioned in the lower portion of the canister to slow down air traveling through the lower portion of the canister. The debris is deposited in the lower portion of the canister, with periodic clean-out required for the debris including opening of the canister and pouring of the debris from the lower portion of the canister. Air is exhausted by being drawn upwards from the lower casing through an open-bottomed cone by a motor and fan located in an upper portion of the cannister. Air is drawn upwards through a one-stage, or a two-stage conical filter held within the cone filter shroud for capture of small particles before the air is evacuated from an exhaust outlet. The cyclonic vacuum generator does not provide a separate, second or third filter media that is interchangeable with secondary filters of different efficiencies, and fails to provide a second or third filter that is removable without displacing the primary, first filter within the filter shroud. Further, the design of the cyclonic vacuum generator fails to provide interchangeable lower portion sections that are dimensioned to provide criticality safe separation of particles while allowing alternate configurations for separations of different particle size distributions in contaminated gas streams. Further, the design of the cyclonic vacuum generator fails to provide a lower, detachable and replaceable, collection container that is sized to maintain accumulated radioactive materials in a criticality safe configuration. A quick disconnect and a replacement collection container, nor a method for rapid interchange of collection containers, is not provided in order to minimize opening of the vacuum device and to minimize leakage of radioactive contamination upon the removal of accumulated debris and particles.
There is a need for a vacuum powered apparatus providing multiple stages of separation of progressively finer particulates from gas mixtures. There is a need for a forced air powered system including at least a first stage of cyclonic flow that precipitates radioactive particles from gas mixtures before a secondary stage of filtration of the gas mixtures in order to eliminate or to minimize the volume and radioactivity content of filter media requiring long-term storage. There is a further need for a vacuum powered apparatus providing multiple stages of separation for radioactive particles, while providing criticality safe geometry for each separation stage and for storage therein. There is an additional need for a vacuum powered system providing a method of operating providing multiple stages of separation for radioactive particles within a portable apparatus that includes adjustable cyclonic lengths and a collection portion that maintains captured radioactive particles in a configuration that minimizes the possibility of an occurrence of a nuclear criticality reaction.
According to one embodiment of the present invention, a vacuum system is provided including an apparatus having multiple stages of removal of particulate entrained in gas while providing criticality safe collection and storage of radioactive particles. Further, a transport vehicle is provided for criticality safe support of the apparatus and for transport of the apparatus containing radioactive particles and potentially fissionable materials. The staged removal of particulates includes ally fissionable materials, from a gas flow induced by a forced air generator incorporated in the apparatus. One use of the apparatus is for collection of radioactive particles having a capacity for initiating nuclear criticality reactions if the particles are not maintained in a volume and shape-limited geometry. The apparatus includes at least two stages of particle separation, including a first filter housing having a gas collection end and a gas exhaust end, with the gas collection end having a diameter less than the diameter of the gas exhaust end. The apparatus includes a cyclone housing releasably attached to the exhaust end of the first filter housing including a filtration media disposed therein for flow of gas through a central channel within the filter housing. The cyclone housing includes a first upper end having a connector flange attached thereto, and having a sufficient upper diameter for insertion therein of the gas collection end of the first filter housing. The cyclone housing is configured in an elongated length that is extended to a particle collection end, with a gas intake port in one side of the cyclone housing. The particle collection end includes a second diameter of a lesser diameter than the first diameter of the first end of the cyclone housing, in order to maintain a cyclonic flow of gas and particles through the cyclone housing for a first stage of separation of particles from the flow of gas. The first stage of particle separation by cyclonic movement of gas and particles provides for collection into the particle collection end of particles having a diameter of greater than about two microns. The flow of gases is counter-current and generally upwards from generally downwards movement of collected particles toward the particle collection end.
The gas collection end of the first filter housing includes a length sufficient to extend from the connector flange of the cyclone housing into the cyclone housing below the gas intake port in the cyclone housing. The opening in the first filter housing gas collection end is configured to have a size-limited geometry for passage of radioactive particles without an occurrence of a criticality reaction. The gas intake port through the cyclone housing wall is positioned below the first end of said cyclone housing, with the intake port positioned at about a mid-portion of the first filter housing when inserted into the cyclone housing. A forced air generator such as a vacuum device and motor, provides a vacuum induced flow of gases through the cyclone housing with induction of a non-linear flow of contaminated gases and particles from the gas intake port, around the lower end of the first filter housing, and generally downwards through a portion of the cyclone housing. After cyclonic swirling of the gases and particles, the gases are induced to flow upwardly into the gas collection end of the first filter housing. The heavier particles are directed downward by cyclonic flow and gravity toward the particle collection end of the cyclone housing. The flow of gases is into the lower end of the first filter housing and toward the vacuum device. The gases are channeled by an internal channel to flow into a perimeter of a first HEPA filter removably supported within the first filter housing. The gas flow is channeled into the perimeter of the HEPA filter, through the HEPA filter media, and out of a central opening of the HEPA, providing a second stage of particle separation from the flow of gas. A third stage of particle separation is provided by a second filtration media removably disposed above the internal channel and above the first filter housing, with the second filtration media providing an internal opening for flow of gas therein and through the second filtration media. The gas flow exits at a perimeter of the second filtration media and exits from a containment housing through gas exhaust vents. The three stages of particle separation provide at least about 99.999% separation of fine particles from a gas stream, while providing internally safe geometry for collected radioactive particles that may have a capacity for initiating nuclear criticality reactions if not maintained in a volume limited geometry.